Tying knots to reliably secure suture is a fundamental skill that students of surgery need to master to become competent surgeons. Knots are needed, for example, for wound closure and attachment of many replacement prosthetic devices, such as, but not limited to replacement aortic valves. Unfortunately, the current ability to assess knot strength and provide feedback to trainees regarding their knot-tying technique is largely subjective. Furthermore, such critique is routinely provided in the operating room environment, which may be ill-suited for objective assessment of a trainee's performance. Even among some surgeons, there is a concern that their knot construction is not optimal.
Optimal knot construction can depend on a variety of factors. When hand-tying knots, for example, a choreographed sequence of suture manipulations must occur in proper order. Appropriate suture tension, which can vary depending on the type of suture being used and/or the type of tissue being sutured, must be maintained throughout the knot formation. As one example, the amount of tension applied by the surgeon to the final “tails” (i.e. free ends of the suture) of a knot significantly alters the degree of slippage, with approximately 80% of the break strength of the suture being preferred during this final step in knot formation. In addition to the magnitude of this applied tension during knot formation, the rate of tension application is also important. For example, a knot's breakage strength is significantly influenced by the rate of application of forces to the tails of the knot. When constant force is applied slowly to the tails of the knot, the resultant knot breakage force tends to be significantly higher than for knots for which the same constant force is applied rapidly to the tails. These, as well as other aspects, are all elements of successful, reliable surgical knot tying for which experience and repetition are needed. Unfortunately, it can be difficult to obtain realistic, objective surgical knot tying experience inside or outside of the operating room.
Further complicating this situation is the increasing prevalence of minimally invasive surgical procedures where tool-augmented hand-tying procedures and minimally invasive instruments are often needed to form knots at surgical sites within a patient, remote from the surgeon. For example, many patients undergo aortic valve replacement surgery. This surgery often involves the need to suture (with accompanying knots) a sewing ring for the prosthetic aortic valve into the aortic root tissue of the patient's heart. If each knotted suture is not tensioned sufficiently, and substantially evenly, then there may be an increased risk of paravalvular leak (PVL). PVL occurs external to the prosthetic valve at the interface between the sewing ring and the underlying cardiac tissue annulus. Even small paravalvular leaks maybe associated with significant morbidity, such as intravascular hemolysis (breakage of a red blood cell's membrane) and anemia as red blood cells are forced through a narrow orifice at very high velocities, and increased risk of death.
PVL affects 5% to 17% of all surgically implanted heart valves. Reoperation is associated with increased morbidity and is not always successful because of underlying tissue breakdown, inflammation, or calcification. Although this is just one surgical example, it is notably very desirable that risk factors contributing to poor surgical procedure outcomes are minimized, and one way to contribute to this goal would be to help surgeons and surgeons-in-training to improve their knot tying skills.
Therefore, it would be very beneficial to have a reliable, reusable, and objective system and method for evaluating surgical knot formation, as well as the formation of multiple inter-related knots (as in the case of an aortic valve replacement), that could effectively be implemented with surgical simulation materials to provide training and teaching opportunities outside of an actual operating room environment.